One use for optical fiber optical power dividers is in the combination of fiber optic communication systems. Where multi-access is required ring systems are particularly economical in comparison with networks with separate links interconnecting every point with every other point. For physically small installations, where the transit line around the ring may be negligible compared with the information rate the advantage of feeding energy in both directions around the ring is that the system will still function after a single break at any place in the ring. One example of an optical power divider can be seen in U.S. application Ser. No. 546,853 now abandoned, filed Feb. 4, 1975 and assigned to the common assignee of the instant invention.
The construction of the divider relies upon the fact that the dominant mode HE.sub.11 has no cut-off wavelength, but as the core size or the core/cladding refractive index difference is reduced more and more of the energy associated with this mode of propagation is carried in the cladding of the fiber waveguide. In the limit, when the core disappears, a plane wave whose normal is the axis of the waveguide is propagating in the cladding. This transformation can be achieved providing the transition is smooth.